Vacuum processing apparatus and operating method therefor

ABSTRACT

This invention relates to a vacuum processing apparatus having vacuum processing chambers the insides of which must be dry cleaned, and to a method of operating such an apparatus. When the vacuum processing chambers are dry-cleaned, dummy substrates are transferred into the vacuum processing chamber by substrates conveyor means from dummy substrate storage means which is disposed in the air atmosphere together with storage means for storing substrates to be processed, and the inside of the vacuum processing chamber is dry-cleaned by generating a plasma. The dummy substrate is returned to the dummy substrate storage means after dry cleaning is completed. Accordingly, any specific mechanism for only the cleaning purpose is not necessary and the construction of the apparatus can be made simple. Furthermore, the dummy substrates used for dry cleaning and the substrates to be processed do not coexist, contamination of the substrates to be processed due to dust and remaining gas can be prevented and the production yield can be high.

This application is a continuing application of application Ser. No.07/751,951, filed Aug. 29, 1991.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a vacuum processing apparatus and operatingmethod therefor. More specifically, the present invention relates to avacuum processing apparatus having vacuum processing chambers the insideof which must be cleaned, and its operating method.

2. Description of the Prior Art

In a vacuum processing apparatus such as a dry etching apparatus, a CVDapparatus or a sputtering apparatus, a predetermined number ofsubstrates to be treated are stored as one unit (which is generallyreferred to as a "lot") in a substrate cassette and are loaded in theapparatus. The substrates after being processed are likewise stored inthe same unit in the substrate cassette and are recovered. This is anordinary method of operating these apparatuses to improve theproductivity.

In such a vacuum processing apparatus described above, particularly inan apparatus which utilizes a reaction by an active gas, as typified bya dry etching apparatus and a CVD apparatus, reaction products adhere toand are deposited on a vacuum processing chamber with the progress ofprocessing. For this reason, problems such as degradation of vacuumperformance, the increase of dust, the drop of the levels of opticalmonitoring signals occur. To solve these problems, conventionally theinsides the vacuum processing chambers are cleaned periodically.Cleaning operations include so-called "wet cleaning" which is wiping-offof the adhering matters by use of an organic solvent, etc., andso-called "dry cleaning" in which an active gas or plasma is used fordecomposing adhering matters. Dry cleaning is superior from the aspectof the working factor and efficiency. These features of the dry cleaninghave become essential with the progress in automation of productionlines.

An example of vacuum processing apparatuses having such a dry cleaningfunction is disclosed in Japanese Utility Model Laid-Open No.127125/1988. This apparatus includes a preliminary vacuum chamber forintroducing wafers to be treated into a processing chamber from anatmospheric side to a vacuum side, which is disposed adjacent to theprocessing chamber through a gate valve, dummy wafers are loaded in thepreliminary vacuum chamber and are transferred into the processingchamber by exclusive conveyor means before the processing chamber issubjected to dry cleaning, and the dummy wafer is returned to the vacuumpreparatory chamber by the conveyor means after dry cleaning iscompleted.

SUMMARY OF THE INVENTION

In the prior art technology described above, the structure of the vacuumprocessing apparatus is not the much the considered. The preliminaryvacuum chamber for storing the dummy wafers must have a large capacity,the exclusive conveyor means is necessary for transferring the dummywafers and thus, the apparatus is complicated in structure.

Dummy wafers used for plasma cleaning are again returned to thepreliminary vacuum chamber and are made to stand by. In this instance,reaction products generated during plasma cleaning and residual gas usedfor plasma cleaning adhere on the used dummy wafers. Thereafter, normalprocessing for wafers is resumed. Therefore, the used dummy wafers andunprocessed wafers exist in mixture inside the preliminary vacuumchamber and this state is not desirable from the aspect of contaminationof unprocessed wafers.

The present invention provides a vacuum processing apparatus whichsolves the problems described above, is simple in structure, preventscontamination of unprocessed substrates and accomplishes a highproduction yield. A vacuum processing apparatus having vacuum processingchambers the insides of which are dry-cleaned after substrates to betreated are processed in vacuum is provided with first storage means forstoring substrates to be treated, second storage means for storing dummysubstrates, the first and second storage means being disposed in theair, conveyor means for transferring the substrates to be processedbetween the first storage means and the vacuum processing chambers andfor transferring the dummy substrates between the second storage meansand the vacuum processing chambers, and control means for controllingthe conveyor means so as to transfer the dummy substrates between thesecond storage means and the vacuum processing chambers before and afterdry cleaning of the vacuum processing chambers. A method of operating avacuum processing apparatus having vacuum processing chambers theinsides of which are dry-cleaned after substrates to be processed areprocessed in vacuum comprises the steps of disposing first storage meansfor storing the substrates to be processed together with second storagemeans for storing dummy substrates in the air atmosphere, transferringthe substrates to be processed between the first storage means and thevacuum processing chambers and vacuum-processing the substrates to beprocessed, and transferring the dummy substrates between the secondstorage means and the vacuum processing chambers before and afterdry-cleaning of the vacuum processing chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a dry etching apparatus as an embodiment of avacuum processing apparatus in accordance with the present invention;and

FIG. 2 is a vertical sectional view taken along line 1--1 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As substrates to be processed are processed in a vacuum processingapparatus, reaction products adhere to and are deposited in vacuumprocessing chambers. The reaction products adhering to and deposited inthe vacuum processing chambers are removed by disposing dummy wafersinside the vacuum processing chambers and by conducting dry-cleaning. Tocarry out dry cleaning, the timings of dry cleaning of the vacuumprocessing chambers are determined and during or after the processing ofa predetermined number of substrates to be processed, dummy substratesare conveyed by substrate conveyor means from dummy substrate storagemeans disposed in the air atmosphere together with processed substratestorage means, and are then disposed inside the vacuum processingchambers. After the dummy substrates are thus disposed, a plasma isgenerated inside each of the vacuum processing chambers to executedry-cleaning inside the vacuum processing chamber. After dry-cleaninginside the vacuum processing chambers is completed, the dummy substratesare returned from the vacuum processing chambers to the dummy substratestorage means by the substrate conveyor means. In this manner, apreliminary vacuum chamber and an exclusive transfer mechanism bothnecessary in prior art techniques become unnecessary, and the apparatusstructure gets simplified. The dummy substrates used for thedry-cleaning and the substrates to be processed do not co-exist insidethe same chamber, so that contamination of substrates to be processeddue to dust and remaining gas is prevented and a high production yieldcan be achieved.

Hereinafter, an embodiment of the present invention will be explainedwith reference to FIGS. 1 and 2.

FIGS. 1 and 2 show a vacuum processing apparatus of the presentinvention which is, in this case, a dry-etching apparatus for etchingwafers, i.e., substrates to be processed by plasma.

Cassette tables 2a to 2c are disposed in an L-shape in this case inpositions such that they can be loaded into and unloaded from theapparatus without changing their positions and postures. In other words,the cassettes 1a to 1c are fixed always in predetermined positions on asubstantially horizontal plane, while the cassette tables 2a and 2b aredisposed adjacent to and in parallel with each other on one of the sidesof the L-shape. The cassette table 2c is disposed on the other side ofthe L-shape. The cassette tables 1a and 1b are for storing unprocessedwafers and for recovering the processed wafers. They can store aplurality (usually 25) of wafers 20 as the substrates to be treated. Thecassette 1c in this case is for storing the dummy wafers for effectingdry-cleaning using plasma (hereinafter referred to as "plasma-cleaning")and recovering the dummy wafers after plasma-cleaning. It can store aplurality of (usually twenty-five pieces) dummy wafers 30.

A load lock chamber 5 and unload lock chamber 6 are so disposed as toface the cassette tables 2a and 2b, and a conveyor 13 is disposedbetween the cassette tables 2a, 2b and the load lock chamber 5 and theunload lock chamber 6. The load lock chamber 5 is equipped with anevacuating device 3 and a gas introduction device 4, and can loadunprocessed wafers in the vacuum apparatus through a gate valve 12a. Theunload lock chamber 6 is similarly equipped with the evacuating device 3and the gas introduction device 4, and can take out processed wafers tothe atmosphere through a gate valve 12d. The conveyor 13 is equippedwith a robot having X, Y, Z and θ axes, which operates so as to deliverand receive the wafers 20 between the cassettes 1a, 1b and the load lockand unload lock chambers 5 and 6 and the dummy wafers 30 between thecassette 1c and the load lock and unload Lock chambers 5 and 6.

The load lock chamber 5 and the unload lock chamber 6 are connected to atransfer chamber 16 through the gate valves 12b and 12c. The transferchamber 16 is rectangular, in this case, and etching chambers 11a, 11band 11c are disposed on the three side walls of the transfer chamber 16through gate valves 15a, 15b and 15c, respectively. A conveyor 14capable of delivering the wafers 20 or the dummy wafers 30 from the loadlock chamber 5 to the etching chambers 11a, 11b, 11c and of deliveringthem from the chambers 11a, 11b, 11c to the unload lock chamber 6 isdisposed inside the transfer chamber 16. The transfer chamber 16 isequipped with an evacuating device 17 capable of independent evacuation.

The etching chambers 11a, 11b, 11c have the same structure and can makethe same processing. The explanation will be given on the etchingchamber 11b by way of example. The etching chamber 11b has a sampletable 8b for placing the wafers 20 thereon, and a discharge chamber isso provided as to define a discharge portion 7b above the sample table8b. The etching chamber 11b includes a gas introduction device 10b forintroducing a processing gas in the discharge portion 7b and anevacuating device 9b for decreasing the internal pressure of the etchingchamber 11b to a predetermined pressure. The etching chamber 11b furtherincludes generation means for generating a microwave and a magneticfield for converting processing gas in the discharge portion 7b toplasma.

A sensor 18 for measuring the intensity of plasma light is disposed atan upper part of the etching chamber. The measured value of the sensor18 is inputted to a controller 19. The controller 19 compares themeasured value from the sensor 18 with a predetermined one anddetermines the timing of cleaning inside the etching chamber. Thecontroller 19 controls the conveyors 13 and 14 to control the transferof the dummy wafers 30 between the cassette 1c and the etching chambers11a to 11c.

In a vacuum processing apparatus having the construction describedabove, the cassettes 1a, 1b storing unprocessed wafers are first placedonto the cassette tables 2a, 2b by a line transfer robot which operateson the basis of the data sent from a host control apparatus, or by anoperator. On the other hand, the cassette 1c storing the dummy wafers isplaced on the cassette table 2c. The vacuum processing apparatusexecutes the wafer processing or plasma cleaning on the basis ofrecognition by itself of the production data provided on the cassettes1a to 1c, of the data sent from the host control apparatus, or of thecommand inputted by an operator.

For instance, the wafers 20 are sequentially loaded in the order fromabove into the etching chambers 11a, 11b, 11c by the conveyors 13 and14, and are etched. The etched wafers are stored in their originalpositions inside the cassette 1a by the conveyors 14 and 13. In thiscase, from the start to the end of the operation, without changing theposition and posture of the cassettes, the unprocessed wafers are takenout from the cassettes and are returned in their original positionswhere the wafers have been stored, and are stored there. In this manner,the apparatus can easily cope with automation of the production line,contamination of the wafers due to dust can be reduced and highproduction efficiency and high production yield can thus beaccomplished.

As etching is repeated, the reaction products adhere to and aredeposited on the inner wall of the etching chambers 11a to 11c.Therefore, the original state must be recovered by removing the adheringmatters by plasma cleaning. The controller 19 judges the timing of thisplasma cleaning. In this case, a portion through which the plasma lightpasses is provided in each of the etching chambers 11a to 11c. Thesensor 18 measures the intensity of the plasma light passing throughthis portion and when the measured value reaches a predetermined one,the start timing of plasma cleaning is judged. Alternatively, the timingof plasma cleaning may be judged by counting the number of wafersprocessed in each etching chamber by the controller 19 and judging thetiming when this value reaches a predetermined value. The actual timingof plasma cleaning that is carried out may be during a processing of apredetermined number of wafers in the cassette 1a or 1b, after theprocessing of all the wafers 20 in a cassette is completed and beforethe processing of wafers in the next cassette.

Plasma cleaning is carried out in the following sequence. In this case,the explanation will be given about a case where the etching chambers11a to 11c are subjected to plasma cleaning by using three dummy wafers30 among the dummy wafers 30 (twenty-five dummy wafers are stored inthis case) stored in the cassette 1c.

Dummy wafers 30 which are stored in the cassette 1c and are not used yetor can be used because the number of times of use for plasma cleaning isbelow a predetermined one are drawn by the conveyor 13. At this time,dummy wafers 30 stored in any position in the cassette 1c may be usedbut in this case, the position numbers of the dun%my wafers in thecassette and their number of times of use are stored in the controller19, and accordingly dummy wafers having smaller numbers of times of useare drawn preferentially. Then, the dummy wafers 30 are loaded in theload lock chamber 5 disposed on the opposite side to the cassette 1a bythe conveyor 13 through the gate valve 12a in the same way as thetransfer at the time of etching of wafers 20. After the gate valve 12ais closed, the load lock chamber 5 is evacuated to a predeterminedpressure by the vacuum exhaust device 3 and then the gate valves 12b and15a are opened. The dummy wafers 30 are transferred by the conveyor 14from the load lock chamber 5 to the etching chamber 11a through thetransfer chamber 16 and are placed on the sample table 8a. After thegate valve 15a is closed, plasma cleaning is carried out in the etchingchamber 11a in which the dummy wafers 30 are disposed, under apredetermined condition.

In the interim, the gate valves 12a, 12b are closed and the pressure ofthe load lock chamber 5 is returned to the atmospheric pressure by thegas introduction device 4. Next, the gate valve 12a is opened and thesecond dummy wafer 30 is loaded in the load lock chamber 5 by theconveyor 13 in the same way as the first dummy wafer 30, and evacuationis effected again by the evacuating device 3 to a predetermined pressureafter closing the gate valve 12a. Thereafter, the gate valves 12b and15b are opened and the second dummy wafer 30 is transferred from theload lock chamber 5 to the etching chamber 11b through the transferchamber 16 by the conveyor 14. Plasma cleaning is started after the gatevalve 15b is closed.

In the interim, the third dummy wafer 30 is transferred into the etchingchamber 11c in the same way as the second dummy wafer 30 and plasmacleaning is carried out.

After plasma cleaning is completed in the etching chamber 11a in whichthe first dummy wafer 20 is placed, the gate valves 15a and 12c areopened. The used dummy wafer 30 is transferred from the etching chamber11a to the unload lock chamber 6 by the conveyor 14. Then, the gatevalve 12c is closed. After the pressure of the unload lock chamber 6 isreturned to the atmospheric pressure by the gas introduction device 4,the gate valve 12d is opened. The used dummy wafer 30 transferred to theunload lock chamber 6 is taken out in the air by the conveyor 13 throughthe gate valve 12d and is returned to its original position in thecassette 1c in which it is stored at the start.

When plasma cleaning of the etching chambers 11b and 11c is completed,the second and third dummy wafers 20 are returned to their originalpositions in the cassette 1c.

In this way, the used dummy wafers 30 are returned to their originalpositions in the cassette 1c and the dummy wafers 30 are always stockedin the cassette 1c. When all the dummy wafers 30 in the cassette 1c areused for plasma cleaning or when the numbers of times of use of thewafers 30 reach the predetermined ones after the repetition of use, thedummy wafers 30 are replaced as a whole together with the cassette 1c.The timing of this replacement of the cassette is managed by thecontroller 19 and the replacement is instructed to the host controlapparatus for controlling the line transfer robot or to the operator.

Although the explanation given above deals with the case where theetching chambers 11a to 11c are continuously plasma-cleaned by the useof three dummy wafers 30 among the dummy wafers 30 in the cassette 1c,other processing methods may be employed, as well.

For example, the etching chambers 11a to 11c are sequentiallyplasma-cleaned by the use of one dummy wafer 30. In the case of suchplasma cleaning, unprocessed wafers 20 can be etched in etching chambersother than the one subjected to plasma cleaning, and plasma cleaning canthus be carried out without interrupting etching.

If the processing chambers are different, for example, there are anetching chamber, a post-processing chamber and a film-formation chamber,and wafers are sequentially processed while passing through each ofthese processing chambers, each of the processing chambers can besubjected appropriately to plasma cleaning by sending dummy wafers 30during the processing of the wafers 20 which are stored in the cassette1a or 2a and drawn and sent sequentially, by passing merely the dummywafers 30 through the processing chambers for which plasma cleaning isnot necessary, and by executing plasma cleaning only when the dummywafers 30 reach the processing chambers which need plasma cleaning.

According to the embodiment described above, the cassette storing thedummy wafers and the cassettes storing the wafers to be processed aredisposed together in the air, the dummy wafers are loaded from thecassette into the apparatus by the same conveyor as the conveyor fortransferring the wafers, at the time of cleaning, and the used dummywafers are returned to their original positions in the cassette. In thisway, a mechanism for conducting exclusively plasma cleaning need not beprovided, and the construction of the apparatus can be simplified. It isnot necessary to handle plasma cleaning as a particular processingsequence, but the plasma cleaning can be incorporated in an ordinaryetching processing and can be carried out efficiently in a series ofoperations.

The dummy wafers used for plasma cleaning are returned to their originalpositions in the cassette placed in the air. Accordingly, the used dummywafers and the wafers before and after processing do not exist mixedlyin the vacuum chamber, so that contamination of wafers due to dust andremaining gas does not occur unlike conventional apparatuses.

The used dummy wafers are returned to their original positions in thecassette and the numbers of times of their use is managed. Accordingly,it is possible to prevent the confusion of the used dummy wafers withthe unused dummy wafers and the confusion of the dummy wafers havingsmall numbers of times of use with the dummy wafers having large numbersof times of use. For these reasons, the dummy wafers can be usedeffectively without any problem when plasma cleaning is carried out.

Furthermore, in accordance with the present invention, the apparatus canhave a plurality of processing chambers and can transfer wafers anddummy wafers by the same conveyor. Since plasma cleaning can be carriedout by managing the timing of cleaning of each processing chamber by thecontroller, the cleaning cycle can be set arbitrarily, dry cleaning canbe carried out without interrupting the flow of the processing, theprocessing can be efficiently made and the productivity can be improved.

As described above, according to the present invention, there areeffects that the construction of the apparatus is simple, the substratesto be processed are free from contamination and the production yield ishigh.

What is claimed is:
 1. A vacuum processing apparatus having vacuumprocessing chambers for which dry cleaning is effected therein aftersubstrates to be processed are processed therein in vacuum, saidapparatus comprising:first storage means for storing said substrates tobe treated and second storage means for storing dummy substrates, saidfirst and second storage means being disposed in the air atmosphere,said second storage means not being disposed in a vacuum; conveyor meansfor transferring both (1) said substrates to be processed between saidfirst storage means and said vacuum processing chambers, and (2) saiddummy substrates between said second storage means and said vacuumprocessing chambers; and control means for controlling said conveyormeans so as to transfer said dummy substrates from said vacuumprocessing chambers to said second storage means respectively before andafter said dry cleaning of said vacuum processing chambers.
 2. A vacuumprocessing apparatus according to claim 1, wherein said conveyor meanscomprises first conveyor means disposed in the air and second conveyormeans disposed in vacuum.
 3. A vacuum processing apparatus according toclaim 1, wherein the apparatus includes a plurality of said vacuumprocessing chambers.
 4. A vacuum processing apparatus according to claim1, wherein said control means includes means for judging the timing ofdry cleaning of said vacuum processing chambers.
 5. A vacuum processingapparatus according to claim 4, wherein judgement of the timing of drycleaning is made by means for counting the number of times of processingof said substrates to be processed in said vacuum processing chambers.6. A vacuum processing apparatus according to claim 1, wherein saidcontrol means includes means to distinguish between the first storagemeans and the second storage means, so as to determine that the secondstorage means contains dummy substrates, and to selectively control theconveyor means to transfer said dummy substrates from said secondstorage means to said vacuum processing chambers and from said vacuumprocessing chambers to said second storage means respectively before andafter said dry cleaning of said vacuum processing chambers, whereby saiddummy substrates stored in said second storage chamber are positioned inthe vacuum processing chambers during said dry cleaning of said vacuumprocessing chambers.
 7. A vacuum processing apparatus according to claim1, further including control means for said dry cleaning, said controlmeans for the dry cleaning causing the dry cleaning to be performedwhile the dummy substrates, transferred from the second storage means bythe conveyor means, are in the vacuum processing chambers.
 8. A vacuumprocessing apparatus according to claim 1, wherein said first storagemeans and said second storage means are separate storage means separatedfrom each other.
 9. A vacuum processing apparatus according to claim 1,further comprising dummy substrates provided in said second storagemeans.
 10. A vacuum processing apparatus according to claim 1, whereinsaid conveyor means is a same conveying system for conveying both thesubstrates and the dummy substrates between respective first and secondstorage means and the vacuum processing chambers.
 11. A vacuumprocessing apparatus according to claim 10, wherein said first storagemeans and said second storage means are separate storage means separatedfrom each other.
 12. A vacuum processing apparatus according to claim 1,wherein each of the first and second storage means includes cassettetables respectively for holding cassettes of the substrates andcassettes of the dummy substrates, and wherein the apparatus furthercomprises cassettes respectively for holding substrates and dummysubstrates on the cassette tables.
 13. A vacuum processing apparatuscomprising:a vacuum processing chamber for processing a substrate to beprocessed in vacuum; means for effecting a dry cleaning in an innerportion of said vacuum processing chamber after said substrate to beprocessed is processed; storage means for storing said substrate to beprocessed and a dummy substrate, said storage means being maintained, atall times during said processing of said substrate to be processed andduring said dry cleaning of said dummy substrate, under an airatmosphere; transfer means for transferring said substrate to beprocessed and said dummy substrate between said storage means and saidvacuum processing chamber; and control means for controlling saidtransfer means to as to transfer selectively said substrate to beprocessed and said dummy substrate from said storage means to saidvacuum processing chamber, such that said substrate to be processed istransferred at a time for said processing to be performed and said dummysubstrate is transferred at a time required to perform said drycleaning.
 14. A vacuum processing apparatus having vacuum processingchambers for which dry cleaning is effected therein after substrates tobe processed are processed therein in vacuum, said apparatuscomprising:first storage means for storing said substrates to be treatedand second storage means for storing dummy substrates, said first andsecond storage means being disposed in the air atmosphere duringduration of processing, in a vacuum, the substrates in said vacuumprocessing chamber; conveyor means for transferring both (1) saidsubstrates to be processed between said first storage means and saidvacuum processing chambers, and (2) said dummy substrates between saidsecond storage means and said vacuum processing chambers; and controlmeans for controlling said conveyor means so as to transfer said dummysubstrates from said second storage means to said vacuum processingchambers and from said vacuum processing chambers to said second storagemeans respectively before and after said dry cleaning of said vacuumprocessing chambers.
 15. A vacuum processing apparatus having vacuumprocessing chambers for which dry cleaning is effected therein aftersubstrates to be processed are processed therein in vacuum, saidapparatus comprising:first storage means for storing said substrates tobe treated and second storage means for storing dummy substrates, saidfirst and second storage means being disposed in the air atmosphere;conveyor means for transferring both (1) said substrates to be processedbetween said first storage means and said vacuum processing chambers,and (2) said dummy substrates between said second storage means and saidvacuum processing chambers, said conveyor means having (a) a firstbuffer means for receiving said substrates to be processed from saidfirst storage means in the air atmosphere and supplying, in vacuum,received substrates to said vacuum processing chamber, and forreceiving, in vacuum, processed substrates from said vacuum processingchamber and supplying received processed substrates to said firststorage means in the air atmosphere, and (b) a second buffer means forreceiving said dummy substrates for cleaning from said second storagemeans in the air atmosphere and supplying, in vacuum, received dummysubstrates to said vacuum processing chamber, and for receiving, invacuum, used dummy substrates from said vacuum processing chamber andsupplying used dummy substrates to said second storage means in the airatmosphere; and control means for controlling said conveyor means so asto transfer said dummy substrates from said second storage means to saidvacuum processing chambers and from said vacuum processing chambers tosaid second storage means respectively before and after said drycleaning of said vacuum processing chambers.
 16. A vacuum processingapparatus comprising:a vacuum processing chamber for processing asubstrate to be processed in vacuum; means for effecting a dry cleaningin an inner portion of said vacuum processing chamber after saidsubstrate to be processed is processed; storage means for storing saidsubstrate to be processed and a dummy substrate, said storage meansbeing maintained, at all times during said processing of said substrateto be processed and during said dry cleaning of said dummy substrate,under an air atmosphere; transfer means for transferring said substrateto be processed and said dummy substrate between said storage means andsaid vacuum processing chamber, wherein said transfer means is fortransferring, under the air atmosphere, said substrates to be processedand said dummy substrates between said storage means and said vacuumprocessing chamber; and control means for controlling said transfermeans to as to transfer selectively said substrate to be processed andsaid dummy substrate from said storage means to said vacuum processingchamber, such that said substrate to be processed is transferred at atime for said processing to be performed and said dummy substrate istransferred at a time required to perform said dry cleaning.
 17. Avacuum processing apparatus having vacuum processing chambers for whichdry cleaning is effected therein after substrates to be processed areprocessed therein in vacuum, said apparatus comprising:first storagemeans for storing said substrates to be treated and second storage meansfor storing dummy substrates, said first and second storage means beingdisposed in the air atmosphere; conveyor means for transferring both (1)said substrates to be processed between said first storage means andsaid vacuum processing chambers, and (2) said dummy substrates betweensaid second storage means and said vacuum processing chambers; andcontrol means for controlling said conveyor means so as to transfer saiddummy substrates from said second storage means to said vacuumprocessing chambers and from said vacuum processing chambers to saidsecond storage means respectively before and after said dry cleaning ofsaid vacuum processing chambers, said control means including means forjudging the timing of dry cleaning of said vacuum processing chambers,judgment of the timing of dry cleaning being made with a sensor formeasuring intensity of plasma light transmitted through said vacuumprocessing chambers.
 18. A vacuum processing apparatus, comprising:atleast one cassette holder, for storing at least one wafer to beprocessed; another cassette holder for storing at least one dummy wafer;wafer locking structure for holding wafers in a gas atmosphere during afirst time period and in a vacuum during a second time period;evacuating structure for evacuating said wafer locking structure; gasintroduction structure for introducing a gas into the wafer lockingstructure; first transfer structure for transferring the at least onewafer to be processed and the at least one dummy wafer between (1) theat least one cassette holder or the another cassette holder and (2) thewafer locking structure, the first transfer structure being under a gasatmosphere; at least one wafer treating chamber for treating the atleast one wafer to be processed in a vacuum; and second transferstructure, adapted to transfer said at least one wafer to be processedand said at least one dummy wafer between said wafer locking structureand said at least one wafer treating chamber, said second transferstructure being adapted to provide said transfer of said at least onewafer to be processed and said at least one dummy wafer between thewafer locking structure and the at least one wafer treating chamberwhile the at least one wafer to be processed and said at least one dummywafer, being transferred by the second transfer structure, aremaintained in a vacuum.
 19. A vacuum processing apparatus according toclaim 18, wherein each of the gas atmospheres is an air atmosphere. 20.A vacuum processing apparatus according to claim 19, wherein the secondtransfer structure is adapted to be provided in a vacuum.
 21. A vacuumprocessing apparatus according to claim 20, wherein said first andsecond transfer structures are separate structures.
 22. A vacuumprocessing apparatus according to claim 18, wherein said at least onecassette holder is for storing at least one wafer to be treated in saidat least one wafer treating chamber.
 23. A vacuum processing apparatusaccording to claim 18, wherein said at least one cassette holder is forstoring at least one wafer which has already been treated in said atleast one wafer treating chamber.
 24. A vacuum processing apparatusaccording to claim 18, wherein said at least one cassette holder isdisposed in an air atmosphere.
 25. A method of operating processingapparatus having at least one wafer treating chamber for treating atleast one wafer to be processed in a vacuum, comprising the stepsof:disposing at least one cassette holder, for storing the at least onewafer, in a gas atmosphere; disposing another cassette holder, forstoring at least one dummy wafer, in a gas atmosphere, the at least onecassette holder and the another cassette holder being cassette holdersof the processing apparatus; and transferring said at least one waferand said at least one dummy wafer between said cassette holders and theat least one wafer treating chamber, by way of a wafer lockingstructure, wherein said wafer locking structure has a gas therein whenthe at least one wafer and the at least one dummy wafer are transferredbetween said cassette holders and said wafer locking structure, andwherein said wafer locking structure has a vacuum therein when said atleast one wafer and said at least one dummy wafer are transferredbetween the at least one wafer treating chamber and said wafer lockingstructure.
 26. A method according to claim 29, including the furtherstep of evacuating said wafer locking structure prior to transferringthe at least one wafer and said at least one dummy wafer between thewafer locking structure and the at least one wafer treating chamber. 27.A method according to claim 26, including the further step ofintroducing said gas into the wafer locking structure when transferringthe at least one wafer and the at least one dummy wafer between thewafer locking structure and said cassette holders.
 28. A methodaccording to claim 29, including the further step of introducing saidgas into the wafer locking structure when transferring the at least onewafer and the at least one dummy wafer between the wafer lockingstructure and said cassette holders.